The use of wireless communications for carrying a variety of information has become widespread in the world today. For example, data, voice, and images (both still and moving) are commonly transmitted by wireless communications means. Such communications are transmitted wirelessly throughout the radio frequency (RF) spectrum.
In order to provide for organized utilization of the RF spectrum, as well as to reduce the potential for conflicting wireless communications within portions of the RF spectrum, a number of bands are typically identified whereby their use is regulated. For example, some bands of RF spectrum may be unlicensed bands, such as may be designated and controlled by a corresponding governmental body, whereby all wireless devices may operate within such a frequency band provided the devices conform to certain restrictions (e.g., meet transmission power limitations, adhere to particular channel requirements, accept interference from other such devices, etc.). Further, some bands of RF spectrum may be licensed bands, such as likewise may be designated and controlled by a corresponding governmental body, whereby only wireless devices operating in accordance with the license holder and conforming to restrictions of the license may operate within such a frequency band.
Wireless communications are utilized on such a scale in many parts of the world that availability of RF spectrum often presents a challenge, whether with respect to communications quality, reliability, and/or availability. Despite efforts to effectively and efficiently regulate the use of spectrum, there are inefficiencies in the utilization of some portions of the RF spectrum. Television (TV) channels, which are typically established from relatively wide frequency bands (e.g., 6 MHz channel bandwidth in the United States and 8 MHz channel bandwidth in Europe and parts of Asia), are provided in licensed bands allocated from a total bandwidth in the hundreds of MHz (e.g., 836 MHz in the United States and 336 MHz in Hong Kong), whereby particular channels are licensed in geographic areas so as to avoid conflict and interference. The typical licensed channel allocation technique often results in one or more unused TV channels (referred to as TV white space (TVWS)) within various geographic areas. Such channels going unused results in inefficient use of the RF spectrum within the corresponding geographic area. However, if such TVWS channels are to be used for other forms of communication (e.g., communications other than the licensed broadcast of TV programming), a white space device (WSD) or TV band device (TVBD) transmitting within a TVWS channel must not interfere with incumbent users of the licensed TV channel.
Two general approaches have been utilized for acquiring TVWS channels, those being geo-location with corresponding TVWS location database and TVWS sensing. According to the geo-location and TVWS location database technique, a WSD utilizes a geo-location detector (e.g., a global positioning system (GPS) location device) to determine its precise geographic location and reports this geographic location information to a TVWS location database for a determination of the TVWS channel(s) predetermined to be available in that particular location. In the TVWS sensing technique, a WSD utilizes a spectrum scanner to determine a list of TV channels which are detected by the WSD and selects one or more undetected TV channels as available TVWS channel(s).
The foregoing techniques are not, however, without disadvantage. For example, the geo-location and TVWS location database technique requires a very accurate location by the WSD (e.g., the Federal Communications Commission (FCC) in the United States requires a location determination to within 50 m accuracy). Although location devices, such as GPS location devices, may be capable of providing highly accurate location determinations, such location determinations are often not possible in particular situations. For example, a WSD disposed indoors or in a location surrounded by tall buildings or other structure causing location signal blockage and/or reflection may be unable to accurately determine position, thereby rendering the WSD incapable of utilizing the geo-location and TVWS location database technique.
As a further example, in using the TVWS sensing technique, the detection of TV channels by a WSD device may provide an unreliable source of data for determining available TVWS channels. In general, such sensing can only detect the presents of TV stations, not TV users. The received signal strength (RSS) of TV channels may vary dozens of dB, even at the same geographic areas, such as due to blockage of signals by mountains and buildings, the sensing device being located indoors/outdoors, higher/lower floors, etc. Accordingly, a WSD may determine a particular channel as being a TVWS channel (e.g., as not having been detected in the spectrum scan due to the WSD being disposed in a coverage shadow), but nevertheless interfere with nearby TV users which are able to receive the particular channel (e.g., as being disposed nearby, outside the coverage shadow), thereby presenting reliability issues with respect to such other users. Additionally, in using the TVWS sensing technique, the sensing threshold for detecting a TV channel is considerable more stringent than the TV service reception threshold (e.g., the FCC in the United States assumes −84 dBm/6 MHz of TV service reception threshold for digital TV (DTV) and −114 DBm/6 MHz for WSD sensing threshold). Accordingly, a particular TV channel may be identified as having been detected by a WSD, thus excluding the TV channel as an available TVWS channel, in locations where the TV channel may nevertheless not be utilized by other TV users, thereby presenting efficiency issues with respect to the utilization of the spectrum.
Various efforts to utilize the foregoing techniques have been proposed. Examples of such efforts may be found in U.S. Pat. No. 8,692,891 (the '891 patent), entitled “System and Method of implementing a TV Band Device with Enhanced Spectrum Sensing,” and United States patent application publication numbers 2014/0148183 (the '183 application), entitled “System and Method for Verifying the Location of a Radio Device”, and 2014/0113670 (the '670 application), entitled “TV White Space Database Assisted Locationing for TV Band Devices”, the disclosures of which are hereby incorporated herein by reference.
The '891 patent utilizes a geo-location detector to determine the precise geographic location of the WSD and reports this geographic location information to a TVWS location database for a determination of the TVWS channel(s) predetermined to be available in that particular location. The WSD device then utilizes a spectrum scanner to scan the list of TVWS channels reported by the TVWS location database to confirm the availability of TVWS channels. Accordingly, this implementation mainly uses the TVWS location database information to rule out prohibited and undetectable channels, whereby the spectrum sensing is only used to verify the feedback information provided by the TVWS location database. The sensing operation employed, however, does not solve the aforementioned issues associated with the TVWS sensing technique.
In the '183 application, spectrum sensing data is utilized to verify the location of the WSD. Accordingly, the WSD utilizes a geo-location detector to determine the precise geographic location of the WSD and reports this geographic location information to a TVWS location database, whereby the TVWS location database identifies a RF footprint prediction for the reported location. The spectrum sensing data provided by the WSD spectrum scanner is correlated with the RF footprint data to verify the reported location of the WSD. The capability for highly accurate location determinations by the WSD, to pinpoint the location of the WSD in order to query the TVWS location database for TVWS channels, remain a requirement of this technique.
The '670 application utilizes trilateration techniques to determine the location of the WSD device. The WSD utilizes information (e.g., RSS and TV station name or channel numbers) of 3 TV transmitters to determine the WSD device location, whereby this location information is utilized by a TVWS location database for a determination of the TVWS channel(s) predetermined to be available in that particular location. Accordingly, the implementation utilizes information of at least 3 TV stations, RSS must be reported to estimate the distance, and special hardware is employed to detect the TV station names. The technique is not applicable when the same TV channel is used by multiple stations in a particular geographic area while the TV station names are unavailable to the WSD.